Under the legacy MHL 1/2 protocol, a local MHL device communicates with a peer MHL device using a legacy MHL (MHL 1/MHL 2) link. The legacy link, in turn, has a half-duplex legacy control bus that enables exchange of control packets between the local and peer MHL devices. Thus, in the legacy MHL 1/2 configuration, the local MHL device, the peer legacy device, as well as the legacy MHL control bus are all configured to operate in half-duplex.
Under the MHL 3 protocol, a local MHL 3 device communicates with a peer MHL 3 device using an MHL 3 link. The MHL 3 link, in turn, has a full-duplex control bus that supports concurrent bi-directional exchange of control packets between the local and peer MHL devices. Thus, a link layer of an MHL 3 device that communicates with the full-duplex MHL 3 control bus operates in full-duplex. However, a full-duplex link layer is not typically compatible with legacy components of a MHL device, such as translation layer circuitry and software, that were originally designed to communicate over a half-duplex link layer. This incompatibility can cause an expensive redesign of these components to ensure compatibility with a half-duplex link layer.